The present disclosure relates to a developing device to be used in an image forming apparatus such as a copier, a printer, a facsimile, and a composite apparatus having functions of those devices, and to an image forming apparatus including the developing device. In particular, the present disclosure relates to a developing device which replenishes a two-component developer including toner and carrier and discharges surplus developer and to an image forming apparatus including the developing device.
In image forming apparatuses, an electrostatic latent image formed on an image carrier including a photosensitive member and the like is developed by a developing device and visualized as a toner image. Examples of the developing device include one employing a two-component developing method in which a two-component developer is used. The developing device of this type includes a developing container in which a two-component developer including toner and carrier is stored, and there are arranged a developing roller for supplying the developer to the image carrier and a stirring member for supplying the developer in the developing container to the developing roller while stirring and conveying the developer.
In the developing device, the toner is consumed by a developing operation. Meanwhile, the carrier remains in the developing device without being consumed. Accordingly, even though the toner and the carrier are stirred in the developing container, the stirring frequency of the carrier increases, which causes deterioration of the carrier. As a result, charging performance of the carrier with respect to the toner is gradually deteriorated.
In this context, there has been proposed a developing device in which deterioration of charging performance of the carrier is suppressed by replenishment of developer including toner and carrier into a developing container and discharge of the developer including the carrier.
The developing device proposed above has the following configuration. Two stirring members each including a rotary shaft and a helical blade helically formed on an outer periphery of the rotary shaft are arranged in parallel with each other in respective conveyance paths. A partition member is provided between the conveyance paths, and communication portions for exchanging developer are provided to both end portions of the partition member. A developer discharge port is provided on a downstream side with respect to the conveyance path in a developer conveying direction. Between the stirring member and the developer discharge port, a discharge regulating member helically formed in a direction reverse to that of the helical blade of each of the stirring members is provided integrally with the rotary shaft. With this structure, when being replenished into the developing container, developer is conveyed to the downstream side of the conveyance path while being stirred by rotation of the stirring members. When the regulating member is rotated in the same direction as that of the stirring members, the regulating member imparts, to the developer, a conveyance force in a direction reverse to the developer conveying direction due to the stirring members. The developer is retained by the conveyance force in the reverse direction on the downstream side of the conveyance path and increased in height. As a result, surplus developer climbs over the regulating member so as to move to the developer discharge port, with the result of being discharged outside.
However, in the developing device proposed above, in accordance with the rotation of the stirring members, a proximity portion at which the helical blade and the regulating member become closest to each other periodically faces the communication portion, and the developer, which has been increased in height by the proximity portion, is periodically conveyed to the communication portion. In other words, this corresponds to fluctuation in amount of developer to be conveyed to the communication portion in accordance with the rotation of the stirring members. Accordingly, an amount of developer to move to the developer discharge port side fluctuates. As a result, there arises a problem that a discharge amount of the developer becomes unstable.